Lattice tower member fatigue and its control using a novel damping scheme

Hangers of a large number of cross arms of L-type, steel lattice towers in TransAlta Utilities Corporation´s system developed fatigue cracks within fifteen years of erection. The flat terrain and relatively thin hangers suggested that the fatigue could be due to wind-induced vibration. Field measurements showed that direct action of the wind on the tower members, rather than conductor motion, was the driving mechanism. Solutions investigated were: heavier hangers, increased bracing, and dampers developed using a full-scale model of a tower section. The dampers were assessed, with strain gauges and accelerometers mounted on the vibration prone members, in a five month field study. The field data showed that, under comparable wind exposure, the dampers reduced the vibration and increased fatigue life to an estimated ten times that of the original design. At this time some 40% of TransAlta´s about 3000 L-towers have been damped